1. Field of the Invention
The present invention relates to a lever-arm displacement-increasing device for use, for example, in a precise positioning device and a sound-generating actuator in the fields of cars, airplanes, high-precision machining, precise measuring apparatuses, and electronic apparatuses.
2. Description of the Related Art
There is a demand for high-power and compact actuators that produce sound, vibration, or displacement. As a displacement-producing element that satisfies this demand, a magnetostrictive actuator has attracted interest which uses a magnetic material having magnetostrictivity and a rigidity higher than that of a piezoelectric material such as PZT, that is, which uses a magnetostrictive material.
In the magnetostrictive actuator, the magnetostrictive material must be greatly displaced in order to produce great acoustic waves or oscillatory waves. However, in order to greatly displace the magnetostrictive material, a control current must be increased. This increases input power, and also increases the size of the actuator itself.
Japanese Unexamined Patent Application Publication No. 5-236595 discloses magnetostrictive displacement-producing devices that overcome the above problems, and that can efficiently produce a high output and a large displacement. A magnetostrictive displacement-producing device according to an embodiment of the invention disclosed in this publication will now be briefly described with reference to FIG. 6.
In a magnetostrictive displacement-producing device shown in FIG. 6, a driving mechanism is constituted by an actuator element 51 serving as a displacement-producing element having magnetostrictivity, a driving coil 52 extending in the longitudinal direction of the displacement-producing element 51, and a support 53 made of a magnetic pole or a permanent magnet and serving as a magnetic-field generating member. When a control current generated by a displacement control circuit (not shown) is applied to the driving coil 52, the driving coil 52 generates a control magnetic field, and the actuator element 51 expands and contracts in response to field changes. When the support 53 is made of an iron magnetic pole, the efficiency of the applied magnetic field can be increased. When the support 53 is a laminate composed of an iron material and a permanent magnet, a magnetic bias can be applied to the actuator element 51, and controllability is enhanced.
The driving mechanism is fixed to a container 54. An action point 61 of a displacement-transmitting jig 60 in a displacement-increasing mechanism is movably attached to a displacing portion of the actuator element 51. A fulcrum 62 of the displacement-transmitting jig 60 provided in view of the lever ratio is pivotally supported by, for example, a pin. A vibrating member 55 of an output section is fixed in contact with an action point 63 of the displacement-transmitting jig 60. The displacement-producing device having the above structure can produce a large displacement and a high output.
However, the displacement-producing device includes many members such as the driving coil 52, the support 53, the actuator element 51, and the displacement-transmitting jig 60. Therefore, the structure is complicated, and the cost is increased.
The operation of the displacement-producing device will be described from the viewpoints of the fulcrum, the force point, and the action point with reference to FIG. 8. The above displacement-increasing mechanism uses a lever. As shown in FIG. 8, the fulcrum of the lever is disposed ahead of the actuator element 51, and cannot be moved toward the peripheral wall and the rear end of the actuator element 51. That is, it is impossible to freely move the fulcrum of the lever.
Japanese Unexamined Patent Application Publication No. 10-201256 discloses a displacement-increasing mechanism having a simple structure in which the fulcrum of the lever is disposed behind the force point in order to overcome the technical problem of the above-described displacement-producing device. The disclosed displacement-increasing mechanism aims to displace an output displacing portion in a direction orthogonal to the displacing direction of an actuator element and to increase the output from the output displacing portion. The displacement-increasing mechanism will be briefly described with reference to FIG. 7. An actuator element 3 is stored in an actuator-holding space 104 provided in the center of a base 100. Vibration displacement and force are produced by applying a voltage to the actuator element 3, and press a force point 118 of a lever 109.
The displacement and force applied to the force point 118 are increased and transmitted to an action-point hinge 117 of the lever 109 according to the lever principle, and turn an output displacing portion 112, which extends in a direction orthogonal to the center axis of the base 100, upward on a fulcrum hinge 116. Consequently, the output displacing portion 112 is displaced in the direction orthogonal to the center axis of the base 100.
The operation of this displacement-increasing mechanism will be described from the viewpoints of the fulcrum, the force point, and the action point with reference to FIG. 9.
In the displacement-increasing mechanism, the action-point hinge is essential in order that the fulcrum may be disposed behind the force point. As a result, the displacement-increasing mechanism cannot have a linear shape, but must be shaped like a box. In order to increase the degree of freedom in positioning the fulcrum, the box must be enlarged. In other words, the housing must be enlarged, and it is necessary to increase the control current or to increase the size of the actuator element in order to move the large housing.